1. Field of the Invention
The present invention is related to a method of producing a semiconductor module sealed with resin and a semiconductor module.
2. Description of Related Art
Semiconductor modules for electronic devices such as mobile phones conventionally have a high frequency circuit including a high frequency semiconductor device and a peripheral circuit formed therein. This requires blocking (a shield against) high frequency noise and the like, and thus, such semiconductor modules are entirely covered with a metal shield case. On the other hand, along with the recent increasing demand for compact electronic devices, there has been an increasing demand for smaller and thinner semiconductor modules.
However, in conventional semiconductor modules, pats (lands) for attaching the metal shield case need to be provided on a module substrate, which is an obstruction to achieving smaller and thinner modules.
In order to overcome the obstruction, there has been proposed an improved semiconductor module without a metal shield case (a metal-shield-case-less structure). Next, a description will be given of the improved semiconductor module with reference to the accompanying drawings. FIG. 34 is a schematic sectional view illustrating a conventional semiconductor module, and FIGS. 35 to 39 are schematic sectional views illustrating a process of producing the semiconductor module illustrated in FIG. 34.
As illustrated in FIG. 34, an improved semiconductor module G includes a module substrate 91, electronic components 92 such as a semiconductor device, a capacitor, and a resistor which are mounted on a top surface (a component-mounting surface) of the module substrate, a sealing resin layer 93 which is formed of resin such as epoxy resin and seals the electronic components 92, and an exterior shield 94 which is formed on a surface of the sealing resin layer 93.
Signal conductors 911 are formed on the component-mounting surface of the module substrate 91, and the electronic components 92 are either connected to the signal conductors 911 via bonding wires Bw or directly connected to the signal conductors 911 via terminals thereof. Inside the module substrate, there is formed a ground line 913, which includes an exposed part in its lower surface. The exterior shield 94 is formed of an electrically conductive material to cover top and side surfaces of the sealing resin layer 93. The exterior shield 94 is in contact with the ground line 913 at parts of side portions thereof facing the module substrate 91. The exterior shield 94 is grounded by being in contact with the ground line 913. In this way, it is possible to block (provide a shield against) an adverse effect (such as high frequency noise) caused by, for example, an electromagnetic field or static electricity.
The improved semiconductor module is produced in the following process. A mounting step is performed to mount the electronic components 92 on a top surface of a collective substrate 910 before it is cut into module substrates 91 (see FIG. 35). Then, by using a conventionally well-known method such as a printing method, a sealing step is performed to form the sealing resin layer 93 which seals the top surface of the collective substrate 910 with an insulating resin such as epoxy resin (see FIG. 36). Here, the collective substrate 910 has a structure such that a plurality of individual module sections (which are to be cut and divided into the module substrates 91) are arranged therein.
Then, a first dicing step is performed to form slits in the sealing resin layer 93 corresponding to boundaries between the individual module sections from the top surface side of the sealing resin layer 93 by using a dicing blade. In the first dicing step, the slits are formed in the sealing resin layer 93, and at the same time, part of the collective substrate 910 is cut off to expose part of the ground line 913 formed inside the collective substrate 910 to the top surface side (see FIG. 37).
By using a conventionally well-known method such as a printing method, electrically conductive paste is charged into the slits formed in the sealing resin layer 93 (a charging step). At this time, the electrically conductive paste charged in the slits is in contact with the ground line 913 of the collective substrate 910. Furthermore, a top surface of the sealing resin layer 93 where the slits formed therein are filled with the electrically conductive paste is coated with the electrically conductive paste (a coating step, see FIG. 38). As illustrated in FIG. 38, the electrically conductive paste is grounded by being charged in the slits and applied to coat the top surface of the sealing resin layer 93 so as to be in contact with the ground line 913. Note that the layer of electrically conductive paste serves as the exterior shield 94 of the semiconductor module G.
A second dicing step is performed to cut the collective substrate 910 at boundary parts between modules, that is, at a center part of each of the slits, which are filled with the electrically conductive paste, by using a dicing blade that is thinner than the width of the slits (a dicing blade that is thinner than the dicing blade used in the first dicing step) (see FIG. 39). Thus, since the dicing blade used in the second dicing step is thinner than the one that is used in the first dicing step, the exterior shield 94 is formed on side surfaces of the completed semiconductor module G (see FIG. 34) after the second dicing step, which makes it possible to securely ground the exterior shield 94 (see JP-A-2004-172176).
FIG. 40 is a plan view illustrating the collective substrate before being cut into the semiconductor modules in the second dicing step. A plurality of semiconductor modules G are produced by cutting the collective substrate 910, where modules are two-dimensionally arranged, by using a dicing blade (a second dicing step).
However, in producing semiconductor modules in this method, in which the slits formed in the first dicing step is filled with the electrically conductive paste, the dicing blade and the electrically conductive paste contact each other over a large area in the second dicing step. The electrically conductive paste charged in the slits contains a metal component, and this causes a heavy burden to be imposed on the dicing blade in cutting the electrically conductive paste in the second dicing step.
Besides, this leads to a high risk of defects resulting from the dicing blade rubbing off or cutting off the exterior shield, which is made of the electrically conductive paste, being exfoliated or cut off due to friction with the dicing blade. In addition, a large amount of electrically conductive paste is removed in the second dicing step. These inconveniences tend to result in low productivity and high cost.